linux-kernel - Re: [PATCH v8 2/3] dt-bindings: PCI: pci-imx6: Add external reference clock input

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Message-ID: <20251027-marbles-tarot-92533cb36e1b@spud>
Date: Mon, 27 Oct 2025 17:06:11 +0000
From: Conor Dooley <conor@...nel.org>
To: Hongxing Zhu <hongxing.zhu@....com>
Cc: "robh@...nel.org" <robh@...nel.org>,
	"krzk+dt@...nel.org" <krzk+dt@...nel.org>,
	"conor+dt@...nel.org" <conor+dt@...nel.org>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	Frank Li <frank.li@....com>,
	"l.stach@...gutronix.de" <l.stach@...gutronix.de>,
	"lpieralisi@...nel.org" <lpieralisi@...nel.org>,
	"kwilczynski@...nel.org" <kwilczynski@...nel.org>,
	"mani@...nel.org" <mani@...nel.org>,
	"shawnguo@...nel.org" <shawnguo@...nel.org>,
	"s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>,
	"festevam@...il.com" <festevam@...il.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 2/3] dt-bindings: PCI: pci-imx6: Add external
 reference clock input

On Mon, Oct 27, 2025 at 06:36:32AM +0000, Hongxing Zhu wrote:
> > -----Original Message-----
> > From: Conor Dooley <conor@...nel.org>
> > Sent: 2025年10月25日 1:07
> > To: Hongxing Zhu <hongxing.zhu@....com>
> > Cc: robh@...nel.org; krzk+dt@...nel.org; conor+dt@...nel.org;
> > bhelgaas@...gle.com; Frank Li <frank.li@....com>; l.stach@...gutronix.de;
> > lpieralisi@...nel.org; kwilczynski@...nel.org; mani@...nel.org;
> > shawnguo@...nel.org; s.hauer@...gutronix.de; kernel@...gutronix.de;
> > festevam@...il.com; linux-pci@...r.kernel.org;
> > linux-arm-kernel@...ts.infradead.org; devicetree@...r.kernel.org;
> > imx@...ts.linux.dev; linux-kernel@...r.kernel.org
> > Subject: Re: [PATCH v8 2/3] dt-bindings: PCI: pci-imx6: Add external reference
> > clock input
> > 
> > On Fri, Oct 24, 2025 at 10:40:12AM +0800, Richard Zhu wrote:
> > > i.MX95 PCIes have two reference clock inputs: one from internal PLL,
> > > the other from off chip crystal oscillator. The "extref" clock refers
> > > to a reference clock from an external crystal oscillator.
> > >
> > > Add external reference clock input for i.MX95 PCIes.
> > >
> > > Signed-off-by: Richard Zhu <hongxing.zhu@....com>
> > > Reviewed-by: Frank Li <Frank.Li@....com>
> > > ---
> > >  Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.yaml | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.yaml
> > > b/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.yaml
> > > index ca5f2970f217c..b4c40d0573dce 100644
> > > --- a/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.yaml
> > > +++ b/Documentation/devicetree/bindings/pci/fsl,imx6q-pcie.yaml
> > > @@ -212,14 +212,17 @@ allOf:
> > >      then:
> > >        properties:
> > >          clocks:
> > > +          minItems: 4
> > >            maxItems: 5
> > >          clock-names:
> > > +          minItems: 4
> > >            items:
> > >              - const: pcie
> > 
> > 1
> > 
> > >              - const: pcie_bus
> > 
> > 2
> > 
> > >              - const: pcie_phy
> > 
> > 3
> > 
> > >              - const: pcie_aux
> > 
> > 4
> > 
> > >              - const: ref
> > 
> > 5
> > 
> > > +            - const: extref  # Optional
> > 
> > 6
> > 
> > There are 6 clocks here, but clocks and clock-names in this binding do not
> > permit 6:
> > |  clocks:
> > |    minItems: 3
> > |    items:
> > |      - description: PCIe bridge clock.
> > |      - description: PCIe bus clock.
> > |      - description: PCIe PHY clock.
> > |      - description: Additional required clock entry for imx6sx-pcie,
> > |           imx6sx-pcie-ep, imx8mq-pcie, imx8mq-pcie-ep.
> > |      - description: PCIe reference clock.
> > |
> > |  clock-names:
> > |    minItems: 3
> > |    maxItems: 5
> > 
> > AFAICT, what this patch actually did is make "ref" an optional clock, but the
> > claim in the patch is that extref is optional. With this patch applied, you can
> > have a) no reference clocks or b) only "ref". "extref"
> > is never allowed. 
> Hi Conor:
> Thanks for your review comments.
> Just same to "extref", the "ref" should be marked as optional clock too.

Right, your commit message should then mention that.

> > Is it supposed to be possible to have "ref" and "extref"?
> > Or "extref" without "ref"?
> > Neither "ref" or "extref"?
> "ref" and "extref" have an exclusive relationship of choosing one of the two,
>  and they cannot all exist simultaneously.

Right, please go test what you've produced, because extref is never
permitted by this binding.

> > I don't know the answer to that question because you're doing things that
> > are contradictory in your patch and the commit message isn't clear.
> > 
> Sorry for causing you confusion.


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